> If the success of RISC architectures taught us anything, it's that replacing simple primitive operations with special-purpose combinations is rarely worth the transistors.
That's not actually the lesson of RISC. The points of RISC (going back to the Radin paper) were: 1> compilers are "now" (i.e. very late 70s/early 80s) better than humans in many cases 2> there were many tradeoffs in implementing CISC instructions that aren't used by lots of programmers and 3> those tradeoffs blocked you from other optimizations (register/cache files, speculative execution etc).
So if you look at the x86, it's a RISC machine with an x86 instruction set implemented in software (microcode)...only it's more than that: the ID and pipeline scheduling reflect an understanding of the high level opcodes typically used by contemporary compilers.
In addition there is plenty of useful stuff to be done that reflects an object level model: pointer boxing/unboxing (look at the RISC-V pointer cache), kernel/ user mode protection, FPUs and GPUs which treat specific kinds of bit representations specially....
As with all engineering it's all about the tradeoffs.
That's not actually the lesson of RISC. The points of RISC (going back to the Radin paper) were: 1> compilers are "now" (i.e. very late 70s/early 80s) better than humans in many cases 2> there were many tradeoffs in implementing CISC instructions that aren't used by lots of programmers and 3> those tradeoffs blocked you from other optimizations (register/cache files, speculative execution etc).
So if you look at the x86, it's a RISC machine with an x86 instruction set implemented in software (microcode)...only it's more than that: the ID and pipeline scheduling reflect an understanding of the high level opcodes typically used by contemporary compilers.
In addition there is plenty of useful stuff to be done that reflects an object level model: pointer boxing/unboxing (look at the RISC-V pointer cache), kernel/ user mode protection, FPUs and GPUs which treat specific kinds of bit representations specially....
As with all engineering it's all about the tradeoffs.